Scale Diagrams and Forces

Defining Scale Diagrams and Forces

• A scale diagram represents a real-world situation, but on a smaller scale. The scale is the ratio of the distance on the diagram to the corresponding actual distance.
• Forces are pushes or pulls that can change an object’s shape or motion. They have both magnitude and direction, and are described as vector quantities.

Using Scale Diagrams to Represent Forces

• Forces can be represented visually using arrow diagrams or scale diagrams.
• The direction of an arrow on a scale diagram represents the direction of the force.
• The length of the arrow represents the magnitude of the force. The scale might be something like 1 cm = 10 N.

Resultant Forces

• The resultant force is the overall force acting on a point or an object that is obtained by vectorially adding all the individual forces acting.
• To find the resultant force from two or more forces acting along the same line, add the forces if they are in the same direction, or subtract them if they are in opposite directions.
• For forces that aren’t along the same line, use scale diagrams, accurately drawing each force as an arrow along a line. Join the beginning of the first force to the end of the last force - this gives the resultant force.

Balanced and Unbalanced Forces

• Balanced forces occur when the resultant force is zero. If an object is stationary, it remains stationary, or if it’s moving, it continues moving at the same speed in the same direction.
• With unbalanced forces, the resultant force is nonzero, meaning an object’s motion will change - it might start moving, stop moving, speed up, slow down, or change direction.

Resolving Forces

• Resolving a force involves dividing a single force into two components acting in different directions. This helps analyse the effect of the force more accurately.
• To resolve forces, use scale diagrams to draw the components at right angles to each other, forming a right-angled triangle.
• Use trigonometry (sine, cosine or tangent) to calculate the size of the components if you know the size of the original force and the angle it makes with the direction of one of the components.

Friction and Air Resistance

• Friction and air resistance are types of force that always act to oppose motion.
• They can be represented in scale diagrams and are often the forces balancing the forward motion force in situations where an object is moving at a constant speed.